1. Field of the Invention
The present invention relates to a method of correcting mask data to correct influence of proximity effect, a method of manufacturing a mask, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, in manufacturing of a semiconductor memory device, an integration density of devices and wires constituting a circuit is increased, and miniaturization of a pattern is advanced. In manufacturing of an RISC (Reduced Instruction Set Computer) processor or the like used as a CPU (Central Processing Unit) for an EWS (Engineering Work Station) or a PC (Personal Computer), in 2002, a gate pattern width of 100 nm or less is required to be realized as a gate pattern width of a transistor.
With miniaturization and complication of a circuit pattern, in a photolithography step in which a pattern on a photomask is transferred onto a semiconductor wafer, a low pattern formation accuracy becomes serious, and improvement of formation accuracy of a micropattern is pursued. As a conventional measure for improving the formation accuracy, a resolution enhancement exposure method called a phase shift mask exposure method which improves the contrast to an image projected on the semiconductor wafer by changing the phase of light transmitting a photomask is proposed. A resolution enhancement exposure method called an oblique incident illumination method is also proposed.
In design of a gate pattern of a semiconductor device such as random logic, in order to reduce manufacturing costs, not only a line width of a gate portion but also a line width of a connected wiring portion which connects a gate and a contact pad to each other is required to be a small width of 150 nm or less. A spacing of patterns is required to be a spacing of patterns which is extremely small, i.e., 200 nm or less.
As a method of forming such a pattern, the following double exposure method (for example, Jpn. Pat. Appln. KOKAI Publication No. 7-106227) is known. That is, an alternating phase shifting mask (alternating phase shifting mask) and a binary mask are sequentially exposed to form a resist pattern, and a slimming process of an underlying film is performed using the resist pattern as a mask. The slimming process is a process called trimming or resist trimming. A double transfer method which forms a first resist pattern, performs a slimming process of an underlying film by using the first resist pattern as a mask, and forms a resist pattern again (for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-359352).
In a photolithography technique, with a decrease in design rule of a film pattern formed on a wafer, it becomes difficult to transfer a design pattern on the wafer in a desired shape and a desired size. A process of correcting a mask shape such that the design pattern is transferred on the wafer in a desired shape and a desired size is called an OPC (Optical Proximity effect Correction) process. This process is essential in a recent lithography technique. Furthermore, a process called an OPC (also referred to as PPC (Process Proximity Correction) process when a process bias is included) process which corrects the mask shape including the process bias generated for various reasons is also used.
In the OPC process, in general, an external edge is divided by using corners of a layout pattern, and correction is performed in units of divided edges (to be referred to as segments hereinafter). An evaluation point called a control point and which typifies an edge is arranged for each segment, and a transfer edge position on the wafer at the position corresponding to the evaluation point is calculated to correct the shape of the mask. This is called model-based OPC.
In general, a short segment very slightly affects an image transferred to the wafer. However, at a position where a change of light intensity is large, a very large correction result is obtained as a local correction result, and the short segment may contrarily deteriorate correction accuracy or may adversely affect mask writing or inspection. For this reason, the short segment must be removed from mask writing data. In addition, with an increase in number of control points, correction process time becomes long, and writing data disadvantageously increases. For this reason, at the present, the length of each segment is limited to a certain length.
For example, a first segment from a corner of a pattern opening is set to be long, and second and subsequent segments are generally set to be shorter than the first segment from the corner of the pattern opening to avoid the following drawback. That is, when the first segment from the corner of the pattern opening is set to be short, the above problem in which a correction value is locally very large is posed. Furthermore, the second and subsequent segments are also carefully set to avoid the above problem.
A correction method called rule-based OPC is known. In this correction method, a mask shape in which a transfer edge position is approximate to a displacement of a target, is calculated by an experiment or a simulation in advance, a rule is determined to correct a design pattern so that the mask shape is created, and the mask shape is corrected by using the rule. For example, when a certain line pattern is corrected, a correction amount depending on the size of a space adjacent to the line pattern is selected by using the rule formed in advance to perform correction.
When the alternating phase shifting mask is used, in a transferred pattern, necking may disadvantageously occur at a position separated from the corner of the pattern opening by a distance smaller than the wavelength of exposure light (for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-42545). In particular, in a gate pattern formed by using the alternating phase shifting mask, a gate size is narrow (i.e., a gate length is short), and a current leak called gate leak occurs to increase a power consumption, thereby causing a critical defect. Therefore, it is very important to correct the necking at high accuracy.
However, in a current OPC technique, it is extremely difficult to correct one local point of the pattern shape, and the necking cannot be completely corrected.
In this manner, in the photolithography technique in manufacturing of a semiconductor integrated circuit, the OPC process is essential. In the alternating phase shifting mask, the necking may occur at a position separated from the corner of the pattern opening by a distance slightly smaller than the exposure wavelength in the transferred pattern, and the necking cannot be corrected at high accuracy disadvantageously.